Flight safety is the number one priority of airlines, followed by in-flight comfort and flight operating cost. Incidents may occur when turbulence is experienced in flight. The consequences range from simple discomfort to loss of control of the aircraft. The detection of these phenomena is therefore a key problem.
The turbulence may be of various origins: wake turbulence, convective turbulence, clear air turbulence (or CAT) and windshear.
Wake turbulence, comprising wake vortices, is dreaded when a lighter aircraft than its predecessor becomes too close to it and when the wind does not rapidly dissipate these “wind vortices”. This happens particularly during take-off and landing, because the runway enhances the hazardous effects.
Convective turbulence is associated with shear between descending and ascending movements in cumulous-type cloud masses passed through, such as cumulo nimbus and tower cumulous clouds. Convective turbulence is localized (in and beneath clouds), and sometimes is difficult to predict. However, depending on the meteorological context, it may be anticipated, and then, in anticipation, the appropriate speed is applied.
Clear air turbulence is due to the energy of the mean wind flux at high altitude, or to the transition between two masses of air moving at different speeds, such as on approaching jet streams. Jet streams are wind currents of small thickness but with an average width of a few tens of kilometers, flowing at high speed around the earth at high altitude. In general encountered at cruise altitudes, clear air turbulence is the most hazardous as it cannot be detected. It sometimes happens that persons not wearing safety belts, such as CFC (Commercial Flight Crew) are seriously injured.
Windshear is due to sudden variations or inversions of wind encountered on approaching certain airports in certain weather conditions, or else rapid variations encountered on approaching or penetrating jet streams. This type of turbulence induces wind gradients which may quite simply make the aircraft stall.
It is crucial to detect turbulence as soon as possible in order to apply the appropriate safety rules. In particular, it is often necessary to reduce the speed of the aircraft to what is called a turbulence speed, so as, on the one hand, to reduce the vibrations of the airplane that are not noticed by the passengers and, on the other hand, to prevent any weakening or sometimes fracture of a structure.
A first solution for detecting turbulence consists in using conventional weather radars. However, this solution has the drawback of detecting only storms and cumulonimbus clouds, but not the other phenomena that do not reflect the radar echoes or do so poorly.
A second solution is to use radars based on infrared techniques or Lidar, enabling certain invisible phenomena to be detected. The drawback is that detection is effected only at very short term.
Another solution for the pilot consists in listening to any radio information coming from preceding airplanes. This solution does make it possible to anticipate turbulence sufficiently early to adopt the speed and flight path that are appropriate. However, this solution relies entirely on the pilot and it increases his workload.
The object of the invention is to alleviate the abovementioned problems by proposing a means which is more rapid, easier and more stable for receiving and processing information coming from preceding aircraft and also allows the pilot to be warned when turbulence is on the point of being encountered.